This invention relates to a press having a press tool and a drive mechanism, and in particular, but not exclusively, is concerned with what is known as "hemming" panels, such as automotive body panels.
FIGS. 1A to 1C of the accompanying drawings illustrate hemming of inner and outer panels. The marginal edge 30 of an outer panel 32 (part of which is shown) is initially upturned at about 90.degree., as shown in FIG. 1A, and is fixed in a jig. An inner panel 34 is then placed over the outer panel 32 and is fixed in the jig, such that the outer edge 36 of the inner panel 34 sits close to the bend between the outer panel 32 and its marginal edge 30. In a "pre-hemming" operation, the marginal edge 30 is bent over at approximately 45.degree., as shown in FIG. 1B. Then, in a "final hemming" operation, the marginal edge 30 of the outer panel 32 is pressed down flat under great pressure against the outer edge 36 of the inner panel 34, as shown in FIG. 1C.
The movement of the final hem tool is important. If the panel were to have straight edges, then movement of the tool in the direction marked 38 in FIG. 1B might be acceptable. However, many body panels have curved edges and in these cases it is desirable to use a curved final press tool to hem a large extent of a curve. However, if the tool moved in a direction 38 in the plane of the paper of FIG. 1B at one location along the edge of the panel, at other locations the movement would be inclined relative to the plane of the paper of FIG. 1B, and there would be undesirable movement between the tool and the marginal edge 30, which would produce an unsatisfactory result. For a satisfactory result, it is desirable that the final hem tool moves vertically, as shown by arrow 40 in FIG. 1B.
A press for performing the pre-hemming and final hemming operations is known from International Patent Application No. WO89/09101 and is illustrated in FIGS. 2 to 4 of the accompanying drawings.
Referring to FIGS. 2 to 4, a pre-hemming tool is illustrated at 5, and a final hemming tool is illustrated at 6. The pre-hemming tool 5 is mounted for movement by a parallelogram mechanism having axes 10, 11, 12, 13 and is driven by a hydraulic piston and cylinder arrangement 22 through a lever 16 pivoted about a fixed pivot 18 and through a linkage 28. The final press tool 6 is mounted on a parallelogram arrangement having axes 17, 18, 19, 20, and the lever 16 forms one of the linkages of this parallelogram arrangement. In FIG. 3, it can be seen that the line connecting the axes 11, 13 of the first parallelogram arrangement is generally at 60.degree. to the horizontal, and therefore the movement of the pre-hemming tool 5 at this stage is approximately at 30.degree. to the horizontal. In FIG. 4, it can be seen that the line connecting the axes 18, 20 of the second parallelogram arrangement is generally horizontal, and therefore the movement of the final hemming tool 6 at this stage is generally vertical.
A problem with the arrangement shown in FIGS. 2 to 4 is that the mechanical advantage between the final hemming tool 6 and the piston and cylinder arrangement 21 is roughly unity, and a piston and cylinder arrangement 21 must therefore be provided which can produce very large forces.
It is an object of the present invention to provide a press which does not need such a large operating force, which is compact, and preferably which can be powered by an electric motor.